A liquid crystal display (LCD) has the advantages of portability, low power consumption, and low radiation, and has been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras and the likes. The LCD utilizes liquid crystal molecules to control light transmissivity of each of pixels of the LCD. The liquid crystal molecules are driven according to external video signals received by the LCD.
A conventional LCD generally employs an inversion driving method to drive the liquid crystal molecules to protect the liquid crystal molecules from decay or damage. The inversion driving method can be frame inversion, row inversion, column inversion, dot inversion, and so on. However, the LCD is prone to exhibit image flicker when the LCD employs one of the above inversion driving methods. This is usually due to an offset effect on a common voltage applied to a common electrode of the LCD.
The image flicker of the LCD can be reduced or even be eliminated via modulating the common voltage. Therefore, a driving circuit of the LCD needs to store optimal values of the common voltages in various conditions to realize modulating the common voltage. That is, programming the driving circuit to store the optimal values of the common voltages is an important step in a fabricating process of the LCD.
FIG. 3 is a top view of a conventional LCD. The LCD 1 includes an LCD panel 11 and a driving circuit 10. The driving circuit 10 is used for driving the LCD panel 11 to display images. The driving circuit 10 includes an electric source input terminal (not labeled), a ground terminal (not labeled), and a plurality of one-time programmable (OTP) units (not shown). The OTP cells are used for storing the optimal values of the common voltages. The values of the common voltages are binary. The OTP cells have various circuit structures. For example, the OTP cells can be made of fuses. When the fuse is burnt out, the corresponding OTP cell represents “1”. When the fuse is not burnt out, the corresponding OTP cell represents “0”. A combination of all the “1” and “0” represents the optimal values of the common voltages.
FIG. 4 is a circuit diagram of a programming circuit of the driving circuit of FIG. 3. The programming circuit 30 includes an input terminal 32, a resistor 33, a capacitor 34, and the driving circuit 10. The resistor 33 is an equivalent resistor of wires. The capacitor 34 has a filtering function. The input terminal 32 is connected to the electric source input terminal of the driving circuit 10 via the resistor 33 and is connected to ground via the capacitor 34. The ground terminal of the driving circuit 10 is connected to ground.
An external high voltage signal is inputted to the input terminal 32, and the high voltage signal is inputted to the driving circuit 10 via the resistor 33. The driving circuit 10 converts the high voltage signal into various logic signals. Some fuses are burnt out, and others are not burnt out according to the logic signals. When all the OTP cells are programmed, the external high voltage signal stops applying to the input terminal 32. Programming the driving circuit is correspondingly finished, and the optimal values of the common voltages are stored in the driving circuit.
However, in practice, the external high voltage signal may increases or decreases suddenly. When this happens, the logic signals may be wrong, some fuses should be not burnt out are burnt out, and some fuses should be burnt out are not burnt out. That is, the optimal values of the common voltages storing in the driving circuit 10 are wrong.
Furthermore, when the external high voltage signal is larger than a normal value thereof, the driving circuit 10 is liable to be damaged.
It is desired to provide an programming circuit which overcomes the above-described deficiencies.